I have a 60mm Coronado Ha filter and both a BF15 and BF30 blocking filter also Coronado. It is used on a TV 85 APO refractor. I did have Meade replace the BF 15 filter because of rust but the BF30 is holding up thus far. All equipment was US produced before Coronado moved facility to Mexico.

I am contemplating upgrading to either a Lunt 100 or 152 with double stacking. Is rust also an issue on some Lunts or have either Coronado or Lunt solved it?

Also....since it seems moisture is a cause of the rust....guess getting between the two elements, I have been using a moisture absorbing device in the case to suck up any moisture. Have others found that to be useful or not?

Thanks all for feedback. Sad that this evidently is still an issue after all these years with both C and L products. Hopefully using a desiccant pack in my case will help. Luckily where I live humidity isn't a big issue like it was where I lived before.

It is known the Lunt uses BG glass (verses an ITF), which is a simple soda lime glass. It seems the KG glasses are susceptible to UV exposure deterioration, and perhaps this UV exposure is some sort of accelerator for glass disease, especially the concentrated exposure near focus. The solution would seem to be coatings to protect the surface from both moisture and UV penetration. I note that Oliver uses a UV/IR blocking coating on his KG3 BelOptik glass filters...

Lunt seems to be well aware of the issue and will send you a new BG element for free as a replacement if the problem develops.

During the winter and in high humidity months I store my blocking filters in a sealed food storage vacuum bag with a desiccant, and have employed UV/IR blocking filters and DERF's ahead of every ITF. So far no problems with ITF failure after 10 years. Prior to using these methods I had 2 failures within two years. It would be interesting to see if these methods would have an effect on the standard BG filter used by Lunt.

The wonder fluid is great stuff. I’ve been using it for years. I can’t attest to it being a cure for the aforementioned glass disease one way or the other. But I use it to clean all my optics. It does claim to protect from fungus etc. I get it from Alpine Astro here in the states.

Christopher

"Our imagination is stretched to the utmost, not, as in fiction, to imagine things which are not really there, but just to comprehend those things which 'are' there.". -Feynman